Rounding of drop-stitch elements

ABSTRACT

The invention relates to a drop-stitch element in which at least one adhesive fold (9, 10) of variable depth is introduced into a flat drop-stitch component (8) such that the outer skin of the drop-stitch component can be folded on one side of the drop-stitch component or, according to the position of the fold, alternately on both sides of the drop-stitch component.

The invention relates to a drop-stitch element according to the characterising clause of patent claim 1, and, to a method for producing a drop-stitch element according to patent claim 10.

In a drop-stitch material, thousands of equally long polyester threads hold together, in parallel, two oppositely disposed materials, also referred to as top and bottom. Owing to its design, this special drop-stitch material is produced in webs. The starting material is open on all sides when viewed perpendicular to the stretched polyester threads and needs to be provided with side walls in order to obtain a closed body. This closed body can be filled with air. These air-filled bodies, due to their structure, are completely flat and do not have any curved elements when viewed along the surface.

Inflatable watercraft, such as kayaks, canoes and surfboards, can be made from drop-stitch material. A typical kayak has a bottom which is adapted to the longitudinal axis of the boat, in such a way that it determines the shape of the boat. The two side walls are adhesively bonded to the outer sides of the bottom.

In the case of this adhesive method, the side walls bulge in a longitudinal direction, that is to say a direction of travel, in line with the shape of the bottom. In this case, the bow and stern are usually relatively tapered, for example tapered in such a manner that a hydrodynamically optimised bow structure can be formed, since a drop-stitch material does not permit tapering due to the nature of the material. The inclination of the side walls is attained by an additional, adhesively bonded outer skin, which, after inflation and the associated spacing between bottom and side wall, comes under tension and maintains the side wall at a stable predetermined angle, which is usually selected such that the boat is wider at the top and narrower at its bottom. The biggest problem of this type of construction is, on the one hand, the air-tightness of the boats and, on the other hand, the enormous manual work required for bringing about adhesive bonding with precision. In order to better illustrate this, the length of the adhesive bonds of a kayak measuring 5 metres in length is described:

A kayak of this type consists, inter alia, of two side walls, to each of which, at the end faces, an end strip is to be adhesively bonded, which corresponds to the drop-stitch thickness. This brings about four side strips with adhesive bonding on the left and on the right sides, adding up to an adhesive length of 20 m. A bottom, likewise having a length of five metres, which is to be adhesively bonded to an end strip on the left and the right sides, results in ten metres of adhesive length. In order to attain good air-tightness, all adhesive bonds have to be sealed off with an additional, second adhesive bond in the form of an adhesive tape which is applied over the first adhesive bond.

This means an adhesive length of a further 60 m, since the first adhesive bond is to be sealed off in each case on the left and right sides. Altogether, in the case of a kayak which is as airtight as possible, consisting of drop-stitch material, approximately 90 running metres of adhesive bonding must be provided, duly applied through manual work. The reason for manual work being that the constantly changing adhesive bonding, progressing in curves, precludes mechanical production.

The great drawback of the adhesive techniques used to date for drop-stitch materials for boats resides in the fact that, owing to the straight surfaces of the drop-stitch structures, only a limited design is possible with regard to the hull. Essentially, only a straight flat bottom is possible, having two straight flat and joined side walls, since the drop-stitch material with its holding threads between the walls naturally aims for straight flat shapes after inflation.

It is thus the object of the invention to provide a drop-stitch element with as few openings—and thus adhesive surfaces—as possible for enhanced air-tightness, permitting rounding of the flat drop-stitch component. A method for the production thereof is a further object of the invention.

These objects are attained by a drop-stitch element according to claim 1 or, respectively, a method for producing a drop-stich element according to claim 10. Advantageous further developments are set out in the subsidiary claims.

The drop-stitch element according to the invention is designed in such a way that at least one fold is introduced into a drop-stitch component. This fold is variable in its depth, that is to say, in the overlap of the parts lying opposite one another as a result of the fold. The overlapping regions of the drop-stitch component, that is to say, the regions of an outer skin which are either the top or the bottom of the drop-stitch material, are adhesively bonded to one another.

According to the invention, the depth of the fold changes according to the position and/or the position of the fold in the drop-stitch element. Irrespective of the depth of the fold, the latter is, however, oriented towards the inner region of the drop-stitch element, or, respectively, the drop-stitch component and is introduced either on one side and/or on both sides, i.e., for example, alternately, or also on other sides of the drop-stitch component.

In a preferred embodiment, the fold starts at the surface, i.e. at the top or bottom of a drop-stitch material of a drop-stitch component, thus having a minimum depth at this point, that is to say, a very small overlapping region of the outer skin. In the further progression of the fold, the depth changes, i.e. increases, so that the overlapping region expands. This continues up to a certain point in the drop-stitch component, at which, consequently, the greatest overlap is provided, running up to that point in a curved manner, a straight-line or linear configuration also being conceivable. As soon as a point is reached, at which the maximum depth of the fold is provided, the depth and thus also the overlap region decrease again in a further curving, straight or linear progression, in order to terminate again at the surface.

In a further embodiment, a plurality of folds are provided in a drop-stitch component, which are introduced lying alongside one another on one side, that is to say, on the top or bottom side of the drop-stitch material. These folds as well are each adhesively bonded to one another.

Wedge-shaped punched-out portions, that is to say, material removed from the drop-stitch material, starting from the top towards the bottom, or vice versa, in a configuration tapering from the outside to the inside, have proved to be particularly advantageous, when a rounded shape of the drop-stitch element, or of the drop-stitch component, also referred to as a drop-stitch body, is desired. The wedge-shaped punched-out portions, in combination with the fold or folds, urge the drop-stitch element into a rounded shape, thus permitting an even more variable design of the drop-stitch element.

For aesthetic, optical and/or haptic reasons, the folds may be covered by a flat blank. For this purpose, for example, a material similar to the top or bottom is adhesively bonded or otherwise fixed above the seam, which is created during the folding process. An even more even surface structure than is in any event achieved by the folds in comparison with a double-bonded structure, known from prior art, can thus be attained.

In a further embodiment, the folds are introduced into the drop-stitch component alternately, that is to say, on both sides. The resulting drop-stitch element thus has, for example, a double hull, since the fold is introduced into and adhesively bonded to the top and bottom of the drop-stitch component.

In order to attain an elongated hull shape of the drop-stitch element, two drop-stitch components, in each case having at least one fold, can be aligned in relation to each other in mirrored fashion, such that a solid element located between the two drop-stitch components, for example, an annular element, is encompassed by the two drop-stitch components and that the latter are kept in spaced apart relationship from one another in at least one, preferably an upper, central region while the lower region preferably forms a continuous flush border or transition between the two drop-stitch elements.

In order to form a pointed stern and a pointed bow, it is preferred if a rigid bow or stern element is fitted to the end faces of the drop-stitch components, at the point where they are at a short distance from one another, that is to say, in a transition region from the tapering upper region towards the lower region. This bow or stern element is encased by a waterproof envelope which is braced on inflation of the drop-stitch components, forming with the bow and stern elements a pointed bow and a pointed stern on the drop-stitch element.

It is particularly preferred if the rigid bow and stern elements are fixed resiliently to the end faces, that is to say, to the bow and/or the stern of the drop-stitch element, or to the drop-stitch components.

A method according to the invention for joining a drop-stitch element is characterised by an adhesive technique. This novel adhesive technique resides in the fact that, for example, a boat which has to date been composed of three independent bodies, namely two side walls and a bottom, is built, according to the invention, by using only one or two drop-stitch bodies. These drop-stitch bodies have fewer adhesive bonds, which improves the air-tightness and brings about a marked reduction in production costs.

A further advantage of the method according to the invention is that these adhesive bonds are freely accessible for any repair work in the event of a leak, whereas in the case of previously applied adhesive methods the defective adhesive bonding points are no longer accessible in the event of damage, since they are covered by an outer skin. With the adhesive technique according to the invention, one side of the drop-stitch body is folded inwards, which results in the buckling of the drop-stitch body. In addition, the inward fold is brought about in a curved progression, which results in a bulging shape of the drop-stitch body.

For a smooth production sequence, two mirror-image, i.e. mirror-symmetrical sides can be assembled to form one part. This design has the advantage that adhesive bonding of a plurality of folds can be performed more easily and more quickly in a left and right individual half.

Punching out on surfaces which require particular rounding, has proved to be very practical. A wedge of the drop-stitch material is removed, that is to say, punched out, and the sides are joined together again, the seam in the drop-stitch material being closed by a cover.

The adhesive bond may be designed with a plurality of adjacent folds which begin at the surface of the drop-stitch material and extend in curved progression to a maximum depth in order to then return again to the drop-stitch surface, which is required, for example, for a belly-shaped rowing boat.

Transport of a particularly long conventional watercraft, which is also known as a so-called surf ski, can become difficult, for which reason, in this case, an inflatable design is appropriate. These very long drop-stitch constructions can be kept dimensionally stable by middle segments. In a light-weight version, the middle segment consists of a robust outer woven cover with an inner, inflatable airtight envelope. However, the middle segment may also consist of only one inflatable plastic cover. A plurality of solid segments are also suitable as middle segments, encompassed by the two side walls.

For optical reasons, folds on the upper surface of boats can also be covered by a covering layer.

Further details are set out in the description of an embodiment, reference being made to the accompanying drawings.

There are shown in:

FIG. 1 a cross-sectional view of a prior art drop-stitch element;

FIG. 2 a cross-section through a drop-stitch element according to the invention;

FIG. 3 a perspective view of a rowing boat;

FIG. 4 a perspective view of folding surfaces;

FIG. 5 a sectional view of a rowing boat;

FIG. 6 a plan view of a rowing boat;

FIG. 7 a blank for a rowing boat;

FIG. 8 a bow of a rowing boat;

FIG. 9 a waterproof envelope at a bow region;

FIG. 10 a rigid bow and stern element;

FIG. 11 a variation of a bow and stern element;

FIG. 12 views of a narrow watercraft;

FIG. 13 a two-part double-hull boat and

FIG. 14 a long watercraft.

FIG. 1 shows a cross-sectional view of a kayak made from a drop-stitch material, manufactured according to the current state of the art, consisting of a left side wall 1, a right side wall 2 and a bottom 3. The side walls and bottom are in each case adhesively bonded in an airtight manner to end strips 4 a, 4 b, 4 c. All adhesive bonds are additionally taped using a sealing tape 5 for better air-tightness. The two side walls have to be maintained stable in their inclined position by means of a bottom layer 6 and inside adhesive bonding 7.

FIG. 2 shows a cross-section through a kayak, which is adhesively bonded using the method according to the invention. The left and right side walls, as well as the bottom, consist of only one drop-stitch component 8. A left fold 9 and a right fold 10, on the inner side of the drop-stitch element, folded inwardly and adhesively bonded, bends the side wall toward the bottom. In the case of this adhesive technique, only one circumferential end strip 4 d is necessary. This makes it possible to reduce to a minimum any air leakage, as well as the adhesive bonding work required for the kayak. In contrast to the state of the art, which requires a large number of adhesive bonds, the error potential during processing of the end strip 4 d is significantly reduced. Also, turn-around times for producing a drop-stitch element, shown here, are substantially reduced as a result of the elimination of a bottom layer 6 and inside adhesive bonding 7, so that, in addition to the simplification of production, clear cost-savings over prior art are ensured.

FIG. 3 shows a perspective view of a rowing boat, in which, next to an upper edge 11, on the inner side, an upper circumferential fold 12 a and a lower circumferential fold 12 b are glued in, as a result of which the inner side of the drop-stitch element is shortened, while the outer side remains unshortened. As a result, the drop-stitch element assumes a rounded shape in sections. Folds 12 a, 12 b terminate in the first quarter of the rowing boat, so that, from there, the two sides of the drop-stitch element remain straight, i.e. non-rounded, thereby forming a straight pointed bow shape 13. A deeper fold 12 b results in a more pronounced rounding in a transition region from the bottom to the side walls than is brought about by the upper fold 12 a in a central region of the side walls. This design is illustrated in FIG. 5 in what follows.

The tapered bow shape according to FIG. 3 is also visible in FIG. 4. Here, a perspective view of the upper fold surface 12 a and the lower fold surface 12 b is shown. While the lower fold 12 b extends to a maximum depth of the drop-stitch wall, thereby causing a considerable kink, the upper fold 12 a is narrower resulting in a slight kink. Both folds follow a calculated curve which is responsible for the belly shape of the rowing boat. They begin at the upper surface of the inner wall 12 c, 12 d and extend to the maximum depth 12 e, 12 f of the drop-stitch element, in order to then return again to the surface of the inner wall in a curved progression. This results in the shape of the rowing boat, which is shown in a perspective view in FIG. 3.

FIG. 5 shows a sectional view through the rowing boat according to one of FIG. 3 or 4 with its two folds 12 a and 12 b. The upper fold 12 a, having a negligible depth, results in a slight kink. The lower fold 12 b is designed deeper than the fold 12 a, so that a more pronounced rounding of the drop-stitch material is brought about, which confers its typical shape to the rowing boat. Beyond the roundings shown in FIGS. 3 and 4 and the varying depths of folds 12 a and 12 b, FIG. 5 already indicates that the rowing boat may also be manufactured from 2 mirror-symmetrical drop-stitch components. This is illustrated by the centrally-positioned bar, which indicates an adhesive point. A two-part embodiment of the drop-stitch element is shown in the following Figures. Reference numeral 33 denotes a covering layer, which covers the folds 12 a, 12 b. Such a covering layer 33 may be used in all embodiments for covering the respective folds.

FIG. 6 shows the rowing boat in plan view with a left half 14 and a right half 15 and the folds 12 a, 12 b. Both halves 14 and 15 and, consequently, also the folds 12 a and 12 b are designed in mirror-symmetrical fashion in relation to one another. Punching-out 15 a is performed for both halves 14 and 15, material removal being carried out in each case, so that an approximately wedge-shaped punched-out portion, shown in FIG. 7 and extending from the outside to the inside, is removed from the drop-stitch material. Prior to adhesive bonding of the folds 12 a, 12 b, the punched-out portion 15 a is joined to the punched-out portion 15 b and sealed by an air-tight cover 15 c.

FIG. 7 shows the blank, i.e. the non-adhesively bonded and unfolded drop-stitch material with the left half 14 of the rowing boat, the right mirror-symmetrical half 15 and the folding surfaces of the folds 12 a, 12 b. The punched-out portions 15 a are shown in a possible initial shape, which is designed to taper from the upper edge 11 towards the bottom of the rowing boat. The punched-out portion 15 a is in each case arranged in the rear region, viewed in the direction of travel of the rowing boat, so that by joining the punched-out portion to the joined punched-out portion 15 b the final shape of the rowing boat with the relatively wide stern and a narrowing bow can be attained, as shown in FIGS. 3, 4 and 5.

FIG. 8 shows the bow with the adhesive bonding according to the method according to the invention, wherein the right side wall comes to rest next to the left side wall, the latter being adhesively bonded to one another. The left end face 16 a of the left side wall and the right end face 16 b of the right side wall form a bow nose having twice the width of the drop-stitch side wall. In addition to twice the width of a drop-stitch side wall, a joining location is provided between the two side walls and therefore also between the two end faces 16 a and 16 b, at which joining location the left half 14 and the right half 15 of the rowing boat converge.

FIG. 9 shows a waterproof envelope 17 as a pointed bow. In order to convert the wide bow nose, brought about by the two end faces of the drop-stitch side walls, into a narrow, pointed bow, a waterproof envelope 17 is provided, which is adhesively bonded to the drop-stitch walls by its rear end 18. The envelope 17 is placed over the end faces 16 a and 16 b and some way further, in an overlapping manner, over the two side walls of the rowing boat and is joined to them by way of adhesive bonding between the inner side of the envelope 17 and the outer side of the respective side wall.

FIG. 10 shows a rigid bow and stern element 19. The rigid bow and stern element 19 is inserted with its two ends into a fastening tube 20 and is pressed continuously forward against the envelope 17 by a spring element, which is located in the fastening tube 20, so that the said envelope 17 stretches. If a solid object is impacted by the watercraft, the rigid bow and stern element 19 is pushed back into the fastening tubes 20, so that the tube length A is shortened to tube length B. In the process, the envelope 17 is shortened and deformed as well. After the impact, the spring element pushes the rigid bow and stern element 19 forward again, so that the envelope 17 is automatically tensioned again and springs back into the tapering configuration (see FIG. 9), which is required for good hydrodynamics.

FIG. 11 shows a perspective side elevation and a plan view of a rigid bow and stern element 19, which is fastened by two tabs 21 to the end faces of the drop-stitch side walls. The rigid bow and stern element 19 is held by and/or guided through the tabs 21 which are each fastened on one side to one of the end faces 16 a and 16 b using, for example, a strut between the end faces 16 a and 16 b of the side walls. After inflation of the side walls, the rigid bow and stern element 19 is braced between the end faces of the side walls and the waterproof envelope 17, so that a fixed structural unit with a pointed bow is brought about. The pointed bow is formed by the envelope 17. The pointed envelope 17, stretched over the rigid bow and stern element 19, extends as an extension of the side walls at the level of the upper edge 11. In a non-inflated state of the drop-stitch element, not shown, the rigid bow and stern element 19 is movably maintained in the tabs, so that it can be folded in the direction of one of the side walls for simplified transport without it having to be completely disassembled. When next used, the rigid bow and stern element is once again urged back into its forward-facing end position, which is bounded by the envelope 17.

The illustrations in FIG. 12 show a particularly long, narrow watercraft in elevation, lateral view and plan view, the side wall 22 of which terminates in the adhesively bonded waterproof envelopes 17 on both sides, that is to say, both on the bow side as well as the stern side, as well as on the starboard and port side. A removable seat 23 is located in the centre and the bow-side section of the boat is stabilized by an inflatable middle segment 24, around which the side walls 22 bend slightly. The stern-side section of the boat is stabilised by two inflatable middle segments 24, which are glued in side-by-side, around which the side walls 22 likewise bend slightly. A further plan view shows an alternative embodiment of the stabilising middle segments. Instead of the inflatable middle segments 24, annular solid elements 25, for example being made of glass fibre or carbon, are incorporated, which provide the necessary stability between the two side walls and at the same time a slightly curved shape of the side walls. Owing to the different dimensioning of the solid elements 25, which are designed with a decreasing diameter from the centre of the watercraft towards the bow and the stern, the desired shape of the watercraft is attained while increasing stability.

A lower fold 12 b begins in the front third of the surface of the inner side 12 c of the side wall 22 and widens in a rounded progression in the centre of the boat up to a maximum depth 12 e. The effects of the depth of the fold have already been described in detail when describing FIGS. 3 to 5.

FIG. 13 shows a two-part double-hull boat in elevation and plan view with a bottom-side fold 26 and a top-side fold 27. The varying depth of both folds along the longitudinal axis of the boat permits the round outline 28 of the floats. The bridge 29 forms part of the inner side wall 30 of the float. In the joined state of the fold, the top-side fold 27 forms the narrow underside of the respective float of the double-hull boat. By joining the top-side fold 27, the upper surfaces, also referred to as tops, of the drop-stitch material adjacent to the left and right of the top-side fold 27 (view according to FIG. 13 at the top) are urged into the shape shown at the top of FIG. 13, at an angle to each other. As a result of the varying depth of the top-side fold 27, the shape shown at the bottom in FIG. 13 is attained, which is narrower on the bow side than on the stern side. In addition to the top-side fold 27, a bottom-side fold 26 is required in order to form a bridge 29, which connects the two floats of the double-hull boat. For this purpose, a bottom-side fold 26, varying in its depth, is incorporated in the starting material on the underside, or, respectively, the bottom of the drop-stitch material. During subsequent joining of the bottom-side fold 26, the bridge 29 angles away from the outline 28 of the float in such a way that it runs approximately parallel to an underlying surface, not shown, on which the two floats are standing. In this way, a double-hull boat can be produced in a simple manner from two drop-stitch components. A design with only one drop-stitch component would also be conceivable.

FIG. 14 shows a long watercraft in an elevation, plan view and side elevation, on which one sits and paddles. It has on its upper side a central fold 31, which brings about a keel 32 on its underside. The keel 32 may vary in depth, due to the altered depth of the fold. A covering layer 33 conceals the underlying fold.

The invention relates to a drop-stitch element, in which at least one adhesively bonded fold of variable depth is introduced into a flat drop-stitch component such that the outer skin of the drop-stitch component can be folded on one side of the drop-stitch component or, according to the position of the fold, alternately on both sides of the drop-stitch component.

LIST OF REFERENCE NUMERALS

-   1 Left side wall -   2 Right side wall -   3 Bottom -   4 a, 4 b, 4 c End strips -   4 d Circumferential end strip -   5 Sealing tape -   6 Bottom layer -   7 Inside adhesive bonding -   8 Drop-stitch part -   9 Left fold -   10 Right fold -   11 Upper edge -   12 a Upper fold -   12 b Lower fold -   12 d, 12 d Surface inner wall -   12 e, 12 f Maximum depth -   13 Bow, tapering -   14 Left half -   15 Right half -   15 a Punched-out portion -   15 b Joined punched-out portion -   15 c Air-tight cover -   16 a Left end face -   16 b Right end face -   17 Waterproof envelope -   18 Rear end -   19 Rigid bow and stern element -   20 Fastening tube -   21 Tabs -   22 Side wall -   23 Seat, removable -   24 Middle segments, inflatable -   25 Solid element -   26 Bottom-side fold -   27 Top-side fold -   28 Round outline -   29 Bridge -   30 Inner side wall -   31 Centre-fold -   32 Keel -   33 Covering layer -   A Length -   B Length 

1. Drop-stitch element, characterised in that at least one fold (9, 10, 12 a, 12 b) of variable depth is adhesively bonded into a flat drop-stitch component (8), wherein the outer skin of the drop-stitch component is folded or folded inwards on one or alternately on both sides of the component (8).
 2. Drop-stitch element according to patent claim 1, wherein the fold (9, 10, 12 a, 12 b) starts at the upper surface of the drop-stitch component (8) and then extends increasingly deeper, in curved progression, to a maximum depth (12 e, 12 f), in order to then terminate, once again in curved progression, at the upper surface.
 3. Drop-stitch element according to patent claim 2, wherein a plurality of adjacent folds (9, 10, 12 a, 12 b) are adhesively bonded into one side of the drop-stitch material.
 4. Drop-stitch element according to any one of the preceding patent claims, wherein wedge-shaped punched-out portions (15 a) are provided, in addition to the folds (9, 10, 12 a, 12 b), in order to urge the drop-stitch body into a rounded shape.
 5. Drop-stitch element according to any one of the preceding patent claims, wherein the fold (9, 10, 12 a, 12 b) is covered by a covering layer (33) and/or a punched-out portion (15 a) is covered by a cover (15 c).
 6. Drop-stitch element according to any one of the preceding patent claims, wherein a double-hull is produced by alternate folding (26, 27).
 7. Drop-stitch element according to any one of the preceding patent claims, wherein by means of a drop-stitch component (8), having at least one fold (12 b), and a second drop-stitch component (8), mirrored with respect to the first, an elongated hull shape is brought about in that the mirrored drop-stitch component (8) stretches around an inflatable or solid element (25).
 8. Drop-stitch element according to patent claim 7, wherein a rigid bow and stern element (19) is fitted to the end face (16 a, 16 b) of the two drop-stitch bodies (8) at the bow and the stern, which bow and stern element is braced in a waterproof envelope (17) after inflation and forms a preferably pointed bow (13) and/or a preferably pointed stern.
 9. Drop-stitch element according to patent claim 8, wherein the rigid bow and stern element (19) in the waterproof envelope (17) is attached, preferably spring-mounted, to the end face (16 a, 16 b) of the drop-stitch body at the bow and stern.
 10. Method for joining a drop-stitch element according to any one of the preceding claims, characterised by an adhesive technique, wherein one side of at least one drop-stitch component (8) is folded and adhesively bonded in the region of the fold (9, 10, 12 a, 12 b).
 11. Method according to claim 10, characterised in that two mirror-identical drop-stitch components (8) are combined to form a drop-stitch element. 